Sensors for multi-valued parameters are known. A typical sensor could, for example, output an analog voltage or current signal whose value changes continuously with the value of the sensed parameter. For digital processing of that signal, the analog signal is typically converted by a known A/D converter to its digital code. When digital outputs are obtained in this manner, each discrete output is unique and thus an absolute indicator of the sensed value. By "absolute" is meant that no two outputs are the same over the desired range, so that each output unambiguously identifies a particular analog value or particular range of analog values.
To minimize errors in decoding sensed outputs it is also known to choose Gray coded digital outputs. The Gray code differs from other encoding schemes in that successive coded characters never differ in more than one bit. For example, in a shaft position encoder that outputs a digital signal to indicate which of the segments the shaft is in, when the shaft moves from segments seven to segment eight, the code must change from that for seven to that for eight As the shaft moves across the segment boundary, if more than one bit has to change, it is possible due to slight mechanical inaccuracies that not all bits will change at exactly the same time. If for example the most significant bit in a BCD code changed before any of the other bits changed, a very large error would result. With the Gray encoding scheme, since only one bit is allowed to change at a time, the error is minimized. Also, ambiguity is reduced when the shaft position is in the line that separates any two segments.
It is also desirable to eliminate the A/D converter, an expensive component, and construct a sensor with plural detectors to directly output the digital signal. To the best of by knowledge, no digital-signal-outputting sensor is known that produces a Gray coded output, such less one that is absolute, that is, without repetition of the coded outputs over the operating range of the sensor. Nevertheless, even without the absolute quality, such sensors can be used to obtain absolute information by recording and/or tracking the sequence of outputs to unambiguously distinguish between two outputs of the name code. This requires additional electronics, which is costly and consumes space.